Purification of nickel electroplating solutions



United States Patent O 3,518,171 PURIFICATION OF NICKEL ELECTROPLATING SOLUTIONS Reuven Merker, Riverdale, N.Y., and Salvatore Lucca, Paramus, N.J., assignors to The Metalux Corporation, Paterson, NJ.

No Drawing. Continuation-impart of application Ser. No. 534,413, Mar. 15, 1966. This application July 24, 1969, Ser- No. 844,643

Int; Cl. C23b 5/08 US. Cl. 20449 3 Claims ABSTRACT OF THE DISCLOSURE Zinc, copper and/or iron impurities ordinarily associated with nickel electroplating baths can be removed from solution by introducing an amount of dimethyldithiocarbamate or dibutyldithiocarbarnate or, preferably, diethyldithiocarbamate of nickel into the electroplating bath suflicient to convert the zinc, copper and/or iron impurities into relatively insoluble metal dimethyldithiocarbamates etc. salt. The insoluble salts may be removed from the electroplating baths by passing the treated solution through a standard filtering system.

This application is a continuation-in-part of application Ser. No. 534,413, filed on Mar. 15, 1966 in the name of the same inventors, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a method for the removal of metallic impurities from aqueous acidic nickel solutions. More particularly, the invention relates to a method of removing zinc, copper, and/ or iron impurities from acid nickel electroplating solutions.

Prior art Plating processes differ in sensitivity to the presence of metallic impurities within the electroplating bath. Thus, for example, while stannate tin is extremely tolerant of most impurities, bright nickel and most zinc plating solutions are sensitive to the presence of impurities. Various means have been devised for purifying aqueous metal solutions by chemical treatment or with the use of mechanical means. One conventional technique, for example, for purifying electroplating solutions is the process known as dummying. This consists of plating for a period of time and usually at low current densities upon cathodes which are not intended for use, such as pieces of scrap sheet metal. This low current density electrolysis plates out metallic impurities and/or decomposes some organic contaminants.

Another method for the removal of contaminants from metal solutions consists of passing the solution, intermittently or continuously, through a filter or a series of such devices. This technique, while satisfactory for insoluble impurities, is not adequate for the removal of dissolved impurities. Problems of this type have been overcome with the use of additive materials which react with or complex with the soluble impurities. An operation of this genral type is disclosed by Michael in US. 3,257,294. While the technique is effective for the removal of soluble metallic impurities, a diflicult problem exists for each individual application in locating a composition that can be added to the metallic solution without further increasing impurity problems and which will preferentially react or complex with the soluble metallic impurities to form relatively insoluble compositions that can be subsequently removed using filtration techniques.

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It is therefore an object of this invention to provide a technique for the removal of soluble zinc, copper and/ or iron impurities from aqueous nickel solutions. It is a further object of the present invention to provide a method for preferentially complexing zinc, copper and/ or iron impurities contained in an aqueous acidic nickel electroplating bath by preferentially complexing or reacting the same and thereafter removing the complexed materials from the nickel electroplating bath.

SUMMARY OF THE INVENTION In accordance with the present invention, it has been found that the soluble zinc, copper and/or iron impurities contained in nickel solutions, in particular aqueous acidic nickel solutions, can be removed from solution -by mixing the solution with an amount of nickel dimethyldithiocarbamate, nickel diethyldithiocarbamate, or nickel dibutyldithiocarbamate corresponding to the general formula wherein R is a methyl, ethyl or butyl radical, these compounds react with or complex with soluble metallic impurities to form materials at least sparingly soluble in the aqueous acidic nickel solution. The insoluble materials are thereafter removed using filtration techniques. In conjunction with conventional filtration techniques involving the continuous or, if so desired, intermittent circulation of a nickel solution from a tank through a filtering chamber or zone, in which a filtering membrane and a material, such as activated carbon and filter aids, are utilized, the present invention contemplates the use of the nickel compounds, preferably nickel diethyldithiocarbamate, to remove metallic impurities from solution through the formation of relatively insoluble compounds or complexes of the impurities which are subsequently trapped within the filter system.

Nickel dialkyldithiocarbamate compositions are known articles of commerce. Metal dialkyldithiocarbamate salts have been previously suggested for use as brighteners in copper and zinc electroplating systems. The metal dialkyldithiocarbamate materials, more particularly the preferred nickel diethyldithiocarbamate composition is prepared following the techniques disclosed by Neal et 'al. in US. 2,406,960, the disclosure of which is herein incorporated by reference. As noted earlier, the removal of soluble metallic impurities, in particular zinc, copper and/ or iron impurities that are normally associated with nickel solutions, occurs by the metallic iron impurities replacing the nickel cation of the nickel dlialkyldithiocarbamate salt and thereby forming compounds or complexes that are substantially insoluble in the aqueous acidic nickel solutions. Thereafter, these substantially insoluble materials are removed from the system by means of filtration techniques. The amount of nickel compound employed in any given system depends upon the amount of impurities sought to be removed and the identity of the impurities. Generally, about one gram mole of the nickel salt will remove one gram mole of divalent metal impurity. The amount of nickel salt needed for any given application will trend upwardly for metal impurities having valences greater than two and downwardly for metal impurities having valences less than two. In most instances, complete removal of the metallic impurities is not necessary as it is normally sought to reduce the impurity level or concentration to a point where the impurities do not seriously interfere with the end use of the aqueous nickel solution.

3 DESCRIPTION OF A FIRST PREFERRED EMBODIMENT A bath solution for plating zinc die castings was prepared. The solution consisted of 4200 gallons of bright nickel solution comprising 40 ounces per gallon of nickel o sulfate, 12 ounces per gallon of nickel chloride and 8 ounces per gallon of boric acid. To this conventional nickel solution was also added about 5% by volume of organic additives for brightening purposes. The temperature of the bath was maintained at about 130 F. and the pH of the solution was maintained at about 4.2. The bath solution was continuously recirculated at a rate of about 4,000 gallons per hour by passing the solution through a filter zone comprising a conventional industrial filter membrane and, upstream thereof, a conventional amount of inert filtering materials (activated carbon and filter aids). The purpose of these materials was to facilitate the operation of the filter membrane. A mixture of 4 pounds of additive material containing about 1,000 grams of nickel dimethyldithiocarbamate was separately prepared. This mixture was added at different intervals to the filtration zone, upstream of the filter membrane. Three samples were withdrawn from the electroplating bath during the course of a 9-hour commercial run. The first sample, denoted A, was taken before the treatment of the solution; the second sample, B, was withdrawn after 2 pounds of the additive material containing the nickel salt were added to the filtration chamber; and finally, sample C was taken after about 8 hours of electrodeposition and after 2 more pounds of the material containing the nickel salt were added upstream of the filter membrane. An analysis, effected by conventional atomic absorption techniques, showed the folowing results:

Sample A Sample B Sample Impurity in Solution:

Copper, p.p.m 40 20 1.0 Zine, p.p.m 30.0 26.0 25.0 Iron, p.p.m 0. 5

1 Not Detected.

DESCRIPTION OF A SECOND PREFERRED EMBODIMENT A 500 gallon bright nickel solution for plating zinc die castings was prepared. The solution comprised 40 ounces per gallon of nickel sulfate, 12 ounces per gallon of nickel chloride and 8 ounces per gallon of boric acid, therein. Four hundred grams of nickel diethyldithiocarbamate were added to the solution and allowed to settle for 3 hours. Then, the solution was filtered back to the Sample A Sample B Impurity in Solution:

Copper, p.p.n1 6 1 Zinc, p.p.m 25 18 Iron, p.p.m 5 1 From the above tabulated results, it can be seen that by the simple addition of the Ni salt, the content of metal ion impurities was considerably reduced with only 400 grams of nickel salt.

What is claimed is:

1. In the process wherein nickel is electrodeposited from an aqueous acidic solution containing nickel ions, wherein the nickel solution is at least periodically fed through a filtration chamber to remove impurities therefrom, and wherein, during use, metallic impurities selected from the group consisting of Zinc, copper and iron build up in solution; the improvement in said process wherein a nickel dialkyldithiocarbamate selected from the group consisting of nickel dimethyldithiocarbamate, nickel diethyldithiocarbamate and nickel dibutyldithiocarbamate is added to the solution in amounts sufiicient to precipitate the metallic impurities, whereby the metallic impurities are filtered out of said solution.

2. The process of claim 1, wherein said nickel dialkyldithiocarbamate is nickel diethyldithiocarbamate and wherein said soluble metallic impurities are recovered in said filtration chamber.

3. The process of claim 2, wherein said filtration chamher is composed of a filter membrane and upstream thereof an amount of inert filtering material and said nickel diethyldithiocarbamate is first introduced into said filtration chamber upstream of said filter chamber.

References Cited OTHER REFERENCES G. D. Thorn et al., The Dithiocarbamates and Related Compounds, pp. 157-164 (1962).

GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 

